This invention relates to vertical cavity surface emitting lasers capable of emitting long-wavelength light and particularly to improved mirror stacks in electrically pumped, long-wavelength vertical cavity surface emitting lasers and to methods of fabrication.
Vertical cavity surface emitting lasers (VCSELs) include first and second distributed Bragg reflectors (DBRs) formed on opposite sides of an active area. The VCSEL can be driven or pumped electrically by forcing current through the active area or optically by supplying light of a desired frequency to the active area. Typically, DBRs or mirror stacks are formed of a material system generally consisting of two materials having different indices of refraction and being easily lattice matched to the other portions of the VCSEL. In conventional VCSELs, conventional material systems perform adequately.
However, new products are being developed requiring VCSELs which emit light having long-wavelengths. VCSELs emitting light having long-wavelengths are of great interest in the optical telecommunications industry. This long-wavelength light can be generated by using a VCSEL having an InP based active region. When an InP based active region is used, however, the DBRs or mirror stacks lattice matched to the supporting substrate and the active region do not provide enough reflectivity for the VCSELs to operate because of the insignificant difference in the refractive indices between the two DBR constituents.
Dielectric mirror stacks can be used for VCSEL applications, but they suffer from poor thermal conductivity. Since the performance of these long-wavelength materials is very sensitive to temperature, the thermal conductivity of the DBRs is very important. At least one of the DBRs must have good thermal conductivity to dissipate the heat generated by the laser.
A metamorphically grown DBR has good thermal conductivity and can be used as a heat conducting DBR, as described in copending United States of America Patent Application entitled xe2x80x9cMethod of Fabricating Long-Wavelength VCSEL and Apparatusxe2x80x9d, filed on Aug. 21, 2000, Ser. No. 09/642,359, and incorporated herein by reference. To provide a practical fabrication process, the top DBR can be grown metamorphically, using the substrate (wafer) for support. However, formation of a second or lower DBR with sufficient reflectivity requires the removal of some or all of the substrate. This removal process can be long and difficult.
Accordingly it is highly desirable to provide electrically pumped long-wavelength VCSELs with good thermal conductivity and methods of fabrication.
It is an object of the present invention to provide new and improved methods of fabricating electrically pumped long-wavelength vertical cavity-surface emitting lasers.
It is another object of the present invention to provide new and improved methods of fabricating electrically pumped long-wavelength vertical cavity surface emitting lasers in which both DBRs are grown using semiconductor procedures.
It is still another object of the present invention to provide new and improved methods of fabricating electrically pumped long-wavelength vertical cavity surface emitting lasers in which a lower epitaxially grown DBR is provided with improved reflectivity.
It is still another object of the present invention to provide new and improved electrically pumped long-wavelength vertical cavity surface emitting lasers.
It is a further object of the present invention to provide new and improved electrically pumped long-wavelength vertical cavity surface emitting lasers incorporating DBRs with materials having good thermal conductivity and refractive indices.
The above objects and others are realized in a method of fabricating an electrically pumped, long-wavelength vertical cavity surface emitting laser including epitaxially growing a stack of alternate layers of a first material and a second material on a compatible substrate. A long wave-length active region is epitaxially grown on the stack and a lasing aperture and current confinement volume are defined in the long wave-length active region. A first mirror stack is formed on the long wave-length active region and portions of one of the first material and the second material are removed to form a high reflectivity second mirror stack.
The above objects and others are further realized in an electrically pumped, long-wavelength vertical cavity surface emitting laser in which a stack of alternate layers of a first epitaxially grown material and a second epitaxially grown material are positioned on a compatible substrate. An epitaxially grown long wave-length active region is positioned on the stack and a lasing aperture and current confinement volume are positioned in the long wave-length active region. A first mirror stack is positioned on the long wave-length active region and portions of one of the first material and the second material are removed to form a high reflectivity mirror stack.